Method and apparatus of selecting MBMS operating frequency for user equipment in a wireless communications system

ABSTRACT

In order to prevent a user equipment, called UE hereinafter, from wasting unnecessary radio resources and occurrence of software failure of the UE, a method of performing an operating frequency transferring request for the UE in a wireless communications system includes reporting a request message to request for transferring to a preferred frequency corresponding to UE interested MBMS services when the UE operates in the CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 60/865,607, filed on Nov. 13, 2006 and entitled “Method and Apparatus for MBMS Frequency Selection in a Wireless Communications System”, the contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and apparatus for a user equipment selecting an operating frequency related to multimedia broadcast multicast services, called MBMS services, in a wireless communications system, and more particularly, to a method and apparatus for a user equipment for properly performing an operating frequency transfer request in a wireless communications system to prevent the user equipment from wasting unnecessary radio resources and occurrence of software failure of the user equipment.

2. Description of the Prior Art

The third generation (3G) mobile telecommunications system has adopted a Wideband Code Division Multiple Access (WCDMA) wireless air interface access method for a cellular network. WCDMA provides high frequency spectrum utilization, universal coverage, and high quality, high-speed multimedia data transmission. The WCDMA method also meets all kinds of QoS requirements simultaneously, providing diverse, flexible, two-way transmission services and better communication quality to reduce transmission interruption rates. To enhance multimedia functions in the 3G mobile telecommunications system, a protocol specification developed by the 3rd Generation Partnership Project (3GPP) provides Multimedia Broadcast Multicast Service (MBMS). MBMS is a point-to-multipoint bearer service and is established on an existing network architecture of the Universal Mobile Telecommunications System (UMTS), utilizing Internet Protocol (IP) packets as a medium. Thus, MBMS allows a single source entity to transmit data to multiple user equipments (UEs) simultaneously.

According to the protocol specification developed by the 3GPP, MBMS offers two delivery modes: MBMS Broadcast delivery mode and MBMS Multicast delivery mode. When interested in a specific MBMS service, the UE needs to order the MBMS service from a Broadcast Multicast Service Center (BM-SC) by establishing a service agreement including specific service provision phases. These two delivery modes have different service provision phases. The service provision phase of MBMS Broadcast delivery mode includes Service announcement, Session Start, MBMS notification, Data Transfer and Session Stop. The service provision phase of MBMS Multicast delivery mode includes Subscription, Service announcement, Joining, Session Start, MBMS notification, Data Transfer, Session Stop and Leaving. For realizing customized services, Joining and Leaving sessions utilized in MBMS Multicast delivery mode enable the BM-SC to execute authorization and payment recording for the UEs at the Joining session. The service provision phases mentioned above are well known in the art, and will not be described in detail.

On the other hand, from the standpoint of radio resource control (RRC), all logical data communication exchange channels, be they for providing data transmission exchange to the UE or for providing RRC layer control signal transmission exchange, are defined in the context of a Radio Bearer (RB). In the UE end, the RB comprises one unidirectional, or a pair of, uplink/downlink logic data transmission exchange channels. In the network end, the RB comprises one unidirectional, or a pair of, uplink/downlink logic data transmission exchange channels. For example, a UMTS Terrestrial Radio Access Network (UTRAN) transmits MBMS configuration to the UE by establishing RBs, and the UE stops receiving MBMS service by releasing the RBs. Besides, according to the RRC protocol specification provided by the 3GPP, an RRC state of the UE can be a disconnection mode or an RRC connection mode. The disconnection mode includes Idle mode, and the RRC connection mode includes CELL_PCH, URA_PCH, CELL_FACH and CELL_DCH states.

When providing the MBMS service, the UTRAN may obtain the number of the UEs ordering the MBMS service via a counting procedure, and can adopt either one of the following two transmission modes: point-to-point (p-t-p) transmission and point-to-multipoint (p-t-m) transmission. The UTRAN utilizes the p-t-m transmission to transfer data if the Broadcast mode is selected. On the contrary, if the Multicast mode is selected, the UTRAN utilizes either the p-t-p transmission or the p-t-m transmission to transfer data according to the number of the UEs. In the p-t-p transmission, transmission between the UEs and the UTRAN utilizes a dedicated channel, and thereby the Node-B establishes one dedicated channel for one UE to transmit data and configuration. Compared with the p-t-p transmission, the p-t-m transmission allows a core network (CN) to provide the data and the configuration for multiple UEs in the same cell simultaneously.

In the protocol specification developed by the 3GPP, three logical channels are defined to transmit corresponding MBMS information: MBMS point-to-multipoint Control Channel (MCCH), MBMS point-to-multipoint Traffic Channel (MTCH), and MBMS point-to-multipoint Scheduling Channel (MSCH). MCCH is utilized to transmit a corresponding MBMS configuration, including MBMS Neighboring Cell Information, MBMS Radio Bearer Information, MBMS Service Information, and other information. MTCH is responsible for transferring service data to the UEs. MSCH is used for notifying the UEs with scheduling information of MBMS services. With MSCH, the UEs are allowed to execute reception only when data begins to be transferred, without needing to keep a receiving state on throughout the whole service process.

Generally speaking, the UTRAN includes two or more carrier frequencies for providing a variety of services for UEs, and the UEs are appropriately distributed on these carrier frequencies. On the other hand, for the UE end, when the MBMS service the UE is interested in, or the state of the joined MBMS service, changes, the UE can perform a frequency selection procedure for following service reception operations. According to the meeting document R2-063613 of the 3GPP (3GPP TSG-RAN WG2 Meeting #56), when the UE receives an information element (IE) “MBMS Preferred frequency information” or an IE “MBMS PL Service Restriction Information,” or when the preferred MBMS service changes, the UE shall perform an MBMS frequency selection procedure for transferring a current operating frequency to a preferred frequency corresponding with an MBMS service prioritized by upper layers, so as to execute reception of the concerned MBMS service. The IE “MBMS Preferred frequency information” is included in a message named “MBMS MODIFIED SERVICES INFORMATION”, and is utilized for notifying the UE of the preferred frequency layer corresponding to the concerned MBMS services. The IE “MBMS PL Service Restriction Information” can be sent to the UE through a Radio Bearer Control message, a CELL UPDATE CONFIRM message or an MBMS GENERAL INFORMATION message, and is utilized for notifying the UE that the UTRAN will not provide any new non-MBMS services on the preferred frequency layer, which means that the preferred frequency layer is currently congested. In other words, if the IE “MBMS PL Service Restriction Information” is not included in the MBMS GENERAL INFORMATION message for the preferred frequency layer, there are still free radio resources available on the preferred frequency layer where the UTRAN can also provide the non-MBMS services.

Additionally, according to the protocol specification developed by the 3GPP, the above Radio Bearer Control message and the CELL UPDATE CONFIRM message are sent on a dedicated control channel (DCCH) for a dedicated UE, and the MBMS GENERAL INFORMATION message is sent on MCCH, which is broadcasted for all UEs in a cell. The Radio Bearer Control message can be a RADIO BEARER RECONFIGURATION message, a RADIO BEARER SETUP message, a RADIO BEARER RELEASE message, a TRANSPORT CHANNEL RECONFIGURATION message or a PHYSICAL CHANNEL RECONFIGURATION message, which are well known by those skilled in the art, and thus not narrated herein.

As the UE operates in different RRC states, the behavior of performing the MBMS frequency selection procedure is also different, and the following is aimed at a situation in which the UE operates in the CELL_DCH state. Initially, if there exists one or more preferred frequencies for services included in a variable MBMS_ACTIVATED_SERVICES, which is stored in the UE, and the latest received CELL UPDATE CONFIRM message or Radio Bearer Control message did not include the IE “MBMS PL Service Restriction Information”, which is sent by the UTRAN on DCCH, the UE can proceed to following frequency selection.

Then, the UE selects a preferred frequency corresponding to the MBMS service(s) prioritized by upper layers as the operating frequency, for which the IE “MBMS PL Service Restriction Information” is not included in the MBMS GENERAL INFORMATION message. Finally, the UE can request that the UTRAN be moved to the preferred frequency by means of the MBMS MODIFICATION REQUEST message.

In some cases, such as when the IE “MBMS PL Service Restriction Information” is included in the MBMS GENERAL INFORMATION message for each preferred frequency corresponding with the MBMS service which the UE is interested in, the UE will fail on selecting the operating frequency. Thus, there is no need for the UE to request to be moved to another frequency in this situation. Requesting to be moved to another frequency in this situation is only a waste of radio resources. Besides, a software error may occur when trying to send the MBMS MODIFICATION REQUEST message because there is no preferred frequency selected. However, according to the above-mentioned meeting document, when the UE operates in the CELL_DCH state and performs the MBMS frequency selection procedure, the UE has to report the MBMS MODIFICATION REQUEST message to the UTRAN no matter whether a preferred frequency corresponding with the MBMS service which the UE is interested in has been successfully selected or not.

SUMMARY OF THE INVENTION

According to the present invention, a method for a user equipment, called UE hereinafter, of a wireless communications system performing an operating frequency transfer request comprises reporting a request message to request for transferring to a preferred frequency corresponding to multimedia broadcast multicast services, called MBMS service hereinafter, the UE is interested in when the UE operates in a CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency.

According to the present invention, a communications device for properly performing an operating frequency transferring request in a wireless communications system to prevent from wasting unnecessary radio resources comprises a control circuit for realizing functions of the communications device; a processor installed in the control circuit, for executing a program code to command the control circuit; and a memory installed in the control circuit and coupled to the processor for storing the program code. The program code comprises reporting a request message to request for transferring to a preferred frequency of a multimedia broadcast multicast service, called MBMS service hereinafter, when the communications device operates in a CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency.

These and other objectives of the present invention will no doubt become obvious to those of ordinary skill in the art after reading the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a communications device.

FIG. 2 is a diagram of the program code shown in FIG. 1.

FIG. 3 is a flowchart diagram of a process according to an embodiment of the present invention.

DETAILED DESCRIPTION

Please refer to FIG. 1, which is a functional block diagram of a communications device 100. For the sake of brevity, FIG. 1 only shows an input device 102, an output device 104, a control circuit 106, a central processing unit (CPU) 108, a memory 110, a program code 112, and a transceiver 114 of the communications device 100. In the communications device 100, the control circuit 106 executes the program code 112 in the memory 110 through the CPU 108, thereby controlling an operation of the communications device 100. The communications device 100 can receive signals input by a user through the input device 102, such as a keyboard, and can output images and sounds through the output device 104, such as a monitor or speakers. The transceiver 114 is used to receive and transmit wireless signals, delivering received signals to the control circuit 106, and outputting signals generated by the control circuit 106 wirelessly. From a perspective of a communications protocol framework, the transceiver 114 can be seen as a portion of Layer 1, and the control circuit 106 can be utilized to realize functions of Layer 2 and Layer 3. Preferably, the communications device 100 is utilized in a third generation (3G) mobile communications system.

Please continue to refer to FIG. 2. FIG. 2 is a diagram of the program code 112 shown in FIG. 1. The program code 112 includes an application layer 200, a Layer 3 202, and a Layer 2 206, and is coupled to a Layer 1 218. The Layer 3 202 includes a radio resource control (RRC) entity 222, which is used for controlling the Layer 1 218 and the Layer 2 206 and performing peer-to-peer RRC communication with other communications devices, such as a base station or a Node-B. In addition, the RRC entity 222 can change an RRC state of the communications device 100, switching between an Idle mode, CELL_PCH, URA_PCH, CELL_FACH or CELL_DCH state.

As for Multimedia Broadcast Multicast Services (MBMS), a UMTS Terrestrial Radio Access Network (UTRAN) can generate RRC messages and information elements (IEs) to include MBMS configuration and then transmit them with a Point-to-Point Radio Bearer (p-t-p RB) or a Point-to-Multipoint Radio Bearer (p-t-m RB) to the communications device 100. In the CELL_DCH state, when the application layer 200 is about to use an MBMS service or the state of a joined MBMS service changes, the RRC entity 222 performs a frequency selection procedure for transferring a current operating frequency to a corresponding carrier frequency to execute following service reception operations. In this situation, the embodiment of the present invention provides an operating frequency transfer request program code 220 to improve an operating frequency transfer request mechanism when the frequency selection procedure is executed in the CELL_DCH state, so as to prevent unnecessary waste of radio resources and software errors. Please refer to FIG. 3, which illustrates a schematic diagram of a process 30 according to an embodiment of the present invention. The process 30 is utilized for a user equipment (UE) of a wireless communications system performing an operating frequency transfer request, and can be compiled into the operating frequency transfer request program code 220. The process 30 includes the following steps:

Step 300: Start.

Step 302: Report a request message to request transfer to a preferred frequency corresponding to an MBMS service the UE is interested in when the UE operates in the CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency; and do not report the request message when the UE has not successfully selected a preferred frequency corresponding to the MBMS services the UE is interested in as the current operating frequency.

Step 304: End.

According to the process 30, the embodiment of the present invention reports a request message to the UTRAN for requesting to be transferred to a preferred frequency corresponding to the MBMS services the UE is interested in when the UE operates in the CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency. Preferably, the process 30 is utilized in an MBMS frequency selection procedure, and the request message is an MBMS MODIFICATION REQUEST message. Thus, when the UE performs the MBMS frequency selection procedure in the CELL_DCH state, the UE will not report the MBMS MODIFICATION REQUEST message to the UTRAN for the situation where no preferred frequency corresponding with the UE interested MBMS services has been selected successfully, so as to save radio resources and prevent occurrence of software failure of the UE.

Therefore, compared with the prior art, the embodiment of the present invention requests the UTRAN to be moved to the preferred frequency by means of the MBMS MODIFICATION REQUEST message only if the UE has successfully selected the preferred frequency corresponding with the MBMS service prioritized by the application layer 200 as a current operating frequency. In this case, when there are no preferred frequencies capable of being selected by the UE, i.e. the IE “MBMS PL Service Restriction Information” is included in the MBMS GENERAL INFORMATION message for each preferred frequency corresponding to all MBMS services the UE is interested in, the embodiment of the present invention need not report the MBMS MODIFICATION REQUEST message to the UTRAN to prevent from causing unnecessary waste of radio resources and software error of the UE.

As mentioned above, in the prior art, when the UE performs the MBMS frequency selection procedure in the CELL_DCH state, the UE has to report the MBMS MODIFICATION REQUEST message to the UTRAN no matter whether a preferred frequency has been successfully selected or not. By comparison, the embodiment of the present invention reports the MBMS MODIFICATION REQUEST message only when the UE has successfully selected a preferred frequency corresponding with the MBMS services the UE is interested in as a current operating frequency. Therefore, the embodiment of the present invention can prevent the UE from wasting unnecessary radio resources and occurrence of software failure of the UE.

Those skilled in the art will readily observe that numerous modifications and alterations of the device and method may be made while retaining the teachings of the invention. Accordingly, the above disclosure should be construed as limited only by the metes and bounds of the appended claims. 

1. A method for a user equipment, called UE hereinafter, of a wireless communications system performing an operating frequency transfer request comprising: reporting a request message to request transfer to a preferred frequency corresponding to multimedia broadcast multicast services, called MBMS services hereinafter, the UE is interested in when the UE operates in a CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency.
 2. The method of claim 1 further comprising: not reporting the request message when the UE has not successfully selected a preferred frequency corresponding to the UE interested MBMS services as a current operating frequency.
 3. The method of claim 1, wherein the request message is a message named “MBMS MODIFICATION REQUEST message”.
 4. The method of claim 1, wherein the wireless communications system is a third generation wireless communications system.
 5. A communications device for properly performing an operating frequency transfer request in a wireless communications system to prevent from wasting unnecessary radio resources, the communications device comprising: a control circuit for realizing functions of the communications device; a processor installed in the control circuit, for executing a program code to command the control circuit; and a memory installed in the control circuit and coupled to the processor for storing the program code; wherein the program code comprises: reporting a request message to request for transfer to a preferred frequency of a multimedia broadcast multicast service, called MBMS service hereinafter, when the communications device operates in a CELL_DCH state and has successfully selected the preferred frequency as a current operating frequency.
 6. The communications device of claim 5, wherein the program code further comprises: not reporting the request message when the communications device has not successfully selected a preferred frequency of the MBMS service as a current operating frequency.
 7. The communications device of claim 5, wherein the request message is a message named “MBMS MODIFICATION REQUEST message”.
 8. The communications device of claim 5, wherein the wireless communications system is a third generation wireless communications system. 